1. Field of the Invention
The present invention relates to a magnetic rotary sensor which detects the absolute positions of the rotation of a rotating body, particularly to a magnetic rotary sensor of the absolute type, which is capable of remarkably improving the resolving power in the detection of the rotational positions of a rotating body.
2. Description of the Related Art
Generally, a magnetic rotary sensor of the absolute type comprises a rotary drum or disc attached to and rotating with a rotating body, on which drum or disc magnetic signals are recorded, and a magnetic sensor composed of magnetoresistive elements and disposed to face a recording portion of the rotary drum or disc. With this arrangement, particular rotational positions of the rotating body can be identified by detecting the magnetic signals by the magnetic sensor, without referring to any reference point. In this case, the output signal of the magnetic sensor is in the form of a digital signal, which represents respective rotational position obtained by equally dividing one rotation of the rotary drum or disc into a predetermined number of positions.
According to the U.S. patent application Ser. No. 560,178 filed on Dec. 12, 1983 and assigned to the same assignee as this application, the recording portion of a rotary drum, which is formed by magnetic material attached on the cylindrical surface of the drum, is divided into plural tracks in the rotational direction of the drum, along which the magnetic signals are recorded in such a manner that codes are formed in the axial direction of the drum. These codes are the digital signals representing the particular positions. The plural tracks are paired, and one pair of the tracks is assigned to record a magnetic signal for one digit of the digital signals.
In the prior art as mentioned above, the minimum interval of the rotational positions to be detected, i.e., the resolving power of a magnetic rotary sensor, is limited by the number of bits of the codes prepared for representing the rotational positions to be detected. If the higher resolving power is required for a magnetic rotary sensor, the number of bits of the codes must be increased by increasing the number of the tracks provided on the recording portion of the drum, with the result that the drum, and hence the magnetic rotary sensor, becomes large in size.